from __future__ import absolute_import, division, unicode_literals from collections import Mapping class Trie(Mapping): """Abstract base class for tries""" def keys(self, prefix=None): keys = super().keys() if prefix is None: return set(keys) # Python 2.6: no set comprehensions return set([x for x in keys if x.startswith(prefix)]) def has_keys_with_prefix(self, prefix): for key in self.keys(): if key.startswith(prefix): return True return False def longest_prefix(self, prefix): if prefix in self: return prefix for i in range(1, len(prefix) + 1): if prefix[:-i] in self: return prefix[:-i] raise KeyError(prefix) def longest_prefix_item(self, prefix): lprefix = self.longest_prefix(prefix) return (lprefix, self[lprefix])